In a few years, NASA and the ESA will conduct the long-awaited Mars Sample Return (MSR) mission. This mission will consist of a lander that will pick up the samples, an ascent vehicle that will send them to orbit, an orbiter that will return them to Earth, and an entry vehicle that will send them to the surface. This will be the first time samples obtained directly from Mars will be returned to Earth for analysis. The research this will enable is expected to yield new insights into the history of Mars and how it evolved to become what we see today.
Returning these samples safely to Earth requires that protective measures be implemented at every step, including transfer, ascent, transit, and re-entry. This is especially true when it comes to the Earth Entry System (EES), the disk-shaped vehicle that will re-enter Earth’s atmosphere at the end of the mission. In addition to a heat shield, engineers at NASA’s White Sands Test Facility (WSTF) near Las Cruces, New Mexico, are busy testing shielding that will protect the vehicle from micrometeorites and space debris during transit back to Earth and during re-entry.
This past week (on Thurs. March 30th), two crew members of Expedition 50 conducted an important spacewalk on the exterior of the International Space Station. During the seven hours in which they conducted this extravehicular activity (EVA), the astronauts reconnected cables and electrical connections on a new Pressurized Mating Adapter (PMA-3) and installed four new thermal protection shields on the Tranquility module.
These shields were required to cover the port that was left exposed when (earlier in the week) the PMA-3 was removed and installed robotically on the Harmony module. In the course of the EVA, the two astronauts – Commander Shane Kimbrough and Flight Engineer Peggy Whitson – were forced to perform an impromptu patch up job when one of the shield unexpectedly came loose.
While things flying off into space is not entirely unusual, on this occasion, there were concerns given the size and weight of the object. This shield measures about 1.5 meters by 0.6 meters (5 feet by 2 feet) and is 5 centimeters (2 inches) thick. It also weighs a little over 8 kg (18 lbs), which would make it a serious impact hazard given the relative velocity of orbital debris (28,000 km/h).
After coming loose, the bundled-up shield quickly floated away and became visible in the distance as a white dot. In response, a team from the Mission Control Center at NASA’s Johnson Space Center began monitoring the shield as it drifted. At the same time, they began working on a contingency plan to substitute the shielding, and advised the astronauts to finish covering the port with the PMA-3 cover Whitson removed earlier that day.
The plan worked, and the cover was successfully installed, providing thermal, micrometeoroid and orbital debris protection for the port. Kimbrough and Whitson finished their EVA at 2:33 pm EDT, having successfully installed the remaining shields on the berthing mechanism port. A few hours after it came loose, Mission Control also determined that the shield posed no risk to the ISS and will eventually burn up in Earth’s atmosphere.
Before concluding their spacewalk, Kimbrough and Whitson also installed what has been nicknamed a “cummerbund” around the base of the PMA-3 adapter. This cloth shield – which also provides micrometeorite protection – is so-named because it fits around the adapter in a way that is similar to how a tuxedo’s cummerbund fits around a person’s waist.
Another highlight of this spacewalk was the fact that Peggy Whitson set two new records with this latest EVA. In addition to setting the record for the most spacewalks by a female astronaut (eight), she also set the record for most accumulated time spent spacewalking – just over 53 hours – by a female astronaut. The 57-year old astronaut now ranks fifth on the list of all-time spacewalking by any astronaut.
On top of all that, Expedition 50 is Whitson’s third mission to the ISS, and she has spent a total of 500 days in space – also a record for any female astronaut. She arrived aboard the ISS aboard the Soyuz MS-03 – along with ESA flight engineer Thomas Pesquet and Roscosmos flight engineer Oleg Novitskiy – and is scheduled to return to Earth in June (though she may remain there until September).
The top spot for most accumulated time in spacewalking is currently held by Russian cosmonaut Anatoly Solovyev, who has participated in 16 spacewalks for a grand total of 82 hours spent in EVA. And in total, spacewalkers have now spent a total of 1,243 hours and 42 minutes performing 199 spacewalks in support of the assembly and maintenance of the ISS.
When it comes to being an astronaut, one of the most important requirements is flexibility – the ability to adapt to unexpected situations and come up with solutions on the fly. Crew 50 and Mission Control certainly demonstrated that this week, maintaining a tradition that brought the Apollo 13 astronauts safely back to Earth and has kept the ISS running for almost two decades.
International Space Station Commander Gennady Padalka and Flight Engineer Yuri Malenchenko completed the first spacewalk of the Expedition 32 mission on Monday, Aug. 20, and successfully completed several tasks, including the installation of micrometeoroid debris shields on the exterior of the Zvezda service module and the deployment of a small science satellite.
Graphic showing the Debris Panel Installation Sites. Credit: NASA
The primary task during the five-hour, 51-minute EVA was to move the Strela-2 cargo boom from the Pirs docking compartment to the Zarya module. The move was another step in preparing Pirs for its eventual undocking and disposal, which will make room for the docking of the new Russian multipurpose laboratory module to the Zvezda nadir port.
This was the 163rd in support of station assembly and maintenance.
A second Expedition 32 spacewalk, scheduled for Aug. 30, will be conducted by NASA Flight Engineer Sunita Williams and Japan Aerospace Exploration Agency Flight Engineer Akihiko Hoshide. This will be the first U.S.-based spacewalk in over a year, since July 2011. During the planned 6.5-hour EVA, the astronauts will replace a faulty power relay unit on the station’s truss, rig power cables for the arrival late next year of a Russian laboratory module, replace a failing robotic arm camera and install a thermal cover on a docking port.